This invention relates to dial indicator calibration devices, and particularly to such a device wherein deflection of a frame weakened at selected points and to which a dial indicator is mounted produces very small linear movements to calibrate and determine limits of resolution of dial indicators.
Dial indicators are widely used in a variety of applications and industries, and typically measure distances or lengths in increments down to thousandths or ten thousandths of an inch, or more recently hundredths or thousandths of a millimeter. These indicators typically use a rack, and reduction gears in conjunction with the rack to move a needle across the face of a dial.
Through use, and sometimes mishandling, the gears become worn and develop lash, meaning that a distance-measuring plunger attached to the rack will move a tiny distance before the needle moves. When this occurs, the indicator is no longer accurate, and must either be refurbished, calibrated or thrown away.
One prior art method for determining whether an indicator is worn or in need of calibration or refurbishing is simply though the use of feeler gages. Here, the indicator is mounted in a fixture with the distance-measuring plunger bearing against a reference surface. A bezel ring (provided on most dial indicators) is set so that the current indication of the indicator is zero, and feeler gages of known thicknesses are placed under the plunger. The reading on the indicator is then compared to the known thickness of the particular gage. Problems with this method is the possibility of debris being trapped between the gage and the reference surface. In addition, where a very high degree of accuracy is desired, a cushion of air may become trapped between the gage and reference surface, making the resulting accuracy uncertain.
Accordingly, it is one object of the invention to provide a calibration apparatus to facilitate calibration of dial indicators. It is another object of the invention to provide a calibration apparatus wherein resolution or sensitivity of the indicator may be determined. Other objects and advantages will become apparent upon a reading of the following specification.
Apparatus for determining resolution of and for calibrating dial indicators is disclosed. A frame having a base is provided with a clamp for mounting a dial indicator to the frame, with a plunger of the dial indicator bearing against a first surface of a selectively movable member. A plunger of a reference indicator against which readings from the dial indicator are compared bears against a second surface of the selectively movable member so that when the selectively movable member is moved, the respective plungers are moved, allowing a comparison between the reference indicator and the dial indicator.